Automatic cibctjit breaker



Nov. 12, 193.5'.l H. c/GRAvEs, JR., 'Er Al. R .119,753

AuTQMATic cmcum'nmxn original Filled Feb. 15, 19:54 2 sheets-smet 2 d# AnoRNEy.

Reissue-d Nav. l12, 193s 1 UNITED STATES Re. 19,753 l x `PATENT voI-Flcs 19.153 l AUTOMATIC CIRCUIT BBEAKEB Herbert C. Graves, Jr.,

East Bradford Township,

Chester County, and Otto Jensen, Glemide, Pa., assignors to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of New Jersey l13 claim.

Our invention relates to automatic electric circuit breakers or circuit interrupters and more particularly to new, improved and simplified op-' short of giving them any or all of the followingV For well-recognized desirable characteristics. example, it is desired that `a circuit interrupter shall lhave a high contact pressure and, at the same time, shall be operable by a relatively small closing force. It is alsov dsirable that a circuit interrupter may be latched in its closed position, thus relieving the usual electromagnetic holding coil oi continuous duty and, at the same time, it is desirable that the operating mechanism shall be completely non-closable or trip-free; that is, that the movable contact maybe operatedinstantly to circuit-opening position under abnormal circuit conditions without hindrance fromy the closing mechanism. It is also desirable that the latching mechanism shall automatically reset and that the breaker may be reclosed after a circuitopening operation by a single movement of the circuit-closing mechanism. l

It is an objectL ofour invention, therefore, to provide a new and improved electric circuit interrupter and more particularly a new and improved operating mechanism therefor which will embody one or more of the above-mentioned delsirable characteristics and which will be simple, reliable in operation, and economical to manufacture.

It is another object of our invention to provide a. new and improved operating mechanism for an electric circuit interrupter in which a high contact pressure may be secured by the use of a. relatively small operating force, and in which the interrupter may be tripped to open-circuit position by a minimum tripping force.

It is a further object of our'inventicn to provide a new and improved operating mechanism for an electric circuit interrupter in which the movable contact is latched in its closed position and is entirely non-closable or trip-free of the closing mechanism. f

Itis a further object of our invention to provide a new and improved operating mechanism for an electric circuit-interrupter in which there is provided a latch mechanism for normally maintaining the interrupter in circuit-closing position and in which the latching mechanism will automatically reset after a tripping operation.

It is a still further object of our invention to provide a new and improved operating mechanism for an electric circuit interrupter in which the closing operation of the nterrupter may be eiectcd, after a tripping operation, by a single movement of the operating mechanism.

(ci. zoo-ss) For a better understanding of our invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings. and its scope will be pointed out in the appended claims.4

In the drawings, Fig. 1 represents a front elevation of our improved electric circuit interrupter embodying our new and improved operating mechanism; Fig. 2 is a cross-sectional view :loY oi the assembly shown in Fig. 1; Figs. 3, 4, 5 and 6 shows details oi the operating mechanism in the several phases of a cycle of operation; and

l Figs. 'I .and 8 illustrate, in detailed perspective,

certain links employed in the operating mechau nism of Figs. 3-6, inclusive.

Referring now more particularly to Figs. 1 and 2 of the drawings, there is illustrated a 3-pole electric circuit interrupter comprising a panel or base member I upon which are mounted the so several stationary contacts 2. Cooperating with each of the several stationary contacts 2 is a movable contact 3 mounted on a pivot l located in the end of a supporting arm E which is clamped upon an insulated shaft 6 Journalled at each 25 end in the brackets 1 and B.' The electric circuit oi' each pair of cooperating contacts 2, 3 is completed through a flexible conductor 9 and a series-connected over-current coil I0, the other terminal of which is similarly connected tow-a stud 30 II or other suitable connector structure emerging at the back of the panel, as illustrated. A wiping spring I2 is preferably interposed between each supporting arm 5 and its associated movable contact 3 to ensure an adequate contact 35 pressure at all times. Suitable bailles or barriers I3 may be -mounted on the panel at both sides of` each pair of cooperating contacts 2 and 3 tol restrict or confine the arc, upon the operation of the interrupter to circuit-opening position, in 40 a well-known manner. Ii desired, magnetic blowout coils I3a may be included in one of the bailles adjacent each pair of cooperating contacts 2-3 and may be connected betweenthe stationary contacts 2 and cooperating studs or connector 45 structures 2u emerging at the hack of the panel.

In order to trip the latching mechanism, which is effective normally to latch the cooperating contacts 2, 3 into circuit-closed position, as described more fully hereinafter, there is provided 50 a tripping shaft I4 also journalled at its end in the brackets 1 and 8 mounted on the panel I. This tripping shaft may be actuated selectively in response to abnormal circuit conditions in any of the circuits including the cooperating pairs of contacts 2 and 3. For this purpose there is associated with each of the series-connected trip coils I0 a magnetic core structure I5 provided with a pivotally mounted magnetic armature I6 suitably biased by its own weight, as illus- 60 trated; or by an auxiliary biasing spring, or by both, if desiredfto a position effecting a gap in the magnetic circuit of its associated coil I0. The auxiliary springs I1a are for the purpose of eliminating rattling of the amature at its hinges. There is also provided a slot I8 in the outer pole member of each of the magnetic cores I5 in which is mounted a trip rod I8, the lower end of which is in the path of movement lof the pivoted armature I8 when moving,` in response to abnormal energization of its coil il, to close the gap in the magnetic circuit of the core I5.

The upper end of the trip rod I9 engages a projection of a clamp mechanism 2l attached to the tripping shaft I4.

Any suitable time-delay mechanism, such as a dash-pot 22, is preferably provided for the tripping mechanism associated with the circuit of each cooperating pair of ycontacts 2 and l. The tripping mechanism, just described, may be adjusted to operate in response to. different magnitudes of overload current by means of an adiusting screw 2l on the time-delay mechanism 22 which is effective to vary the lower position cf the pivoted armature I 5, and thus the value of current ilowing in the coil IU which is adequate to lift the armature I5 against the force.

of gravity. A guide slot 24 in a strip 25 secured to the dash-pot 22 ngages a projection 28 on the trip-rod I8 and mits the lower position of this trip-rod to such a point that the armature falls substantially below its lower end, as shown in Fig. 2, so that the armature I8 has a striking action as it is attracted by the core member I5 to close the gap in the magnetic circuit.

In case it is desirable to trip the circuit interrupter at will or in response to any other predetermined operation or condition, and independently of the overload tripping apparatus described above, there may be provided an additional tripping coil 21 connected to a pair of terminals 28 and provided with a magnetic core member 29 with which cooperates a movable armature and trip-rod engaging'a tripping arm 20 mounted on the shaft I4 in a manner similar to that of the above-described tripping mechanisms. It will be understood that the terminals may be connected to any suitable circuit in response to the energization of which it is desired that the circuit interrupter shall be tripped.

Our improved circuit interrupter. may be operated to circuit-closing position either manually or electromagnetically, although wehave illustrated an electromagnet Vcomprising a stationary magnetic core member 30 and a lcoll 3|, connected to terminals 32, as one means of effecting this operation. 'I'he operating, latching, and tripping mechanisms are enclosed within the housing a portion of which may be integral with the bracket 1. These latter mechanisms are shown in more detail in Figs. 3, 4, 5 and 6. Referring more 'particularly to' Fig. 3,

in which the operating mechanism is vshown in the position corresponding to circuit-opening position of the circuit interrupter, the electromagnet Iii-3| being deenergized, there is shown an operating crank 40 engaging the operating shaft 5 of theseveral movable contacts 3 and normally biased against a stop 4I by any suitable biasing means, such as a spring 42, one end of which is connected to the arm 40, as at the pin 55, and the other terminal of which may be attached to any stationary portion of the operating mechanism or its housing. There is also provided a latch-` ing mechanism comprising a bell-crank 4I havdetent engaging a latching member 45 clamped tol the tripping shaft I4 by any suitable clamping mechanism 41. interconnects the latching member 45, or some portion of its clamping mechanism, and a pin 48 disposed on the bell-crank 43, and serves to secure the engagement of the detent 45 and the latch member 46. l0

The bell-crank 43 is supported in the housing 33 by a pivot 50, which forms a suitablesup- 'port for the stationary terminal 'of the biasing spring 42. Interconnecting the other arnr 5I of the bell-crank 43 and the operating crank 40 l5 of the circuit-interrupting mechanism is a force multiplying, or linkage, mechanism, `such as a toggle mechanism, comprising a pair of links 52 and a link 53, shown more clearly in Figs. 7 and 8, hinged-together by a pivot pin 54 and con- 20 nected to the arm 40 by a pivot pin 55 and to the arm 5| of the crank 43 by a pivot pin 56. The links 52 are provided with extensions 52a which cooperate with stops 53a on the link 58 to limit the upward movement of the hinge of the toggle 25 mechanism. The electromagnet 30, 3| is provided with a movable armature -51, reciprocable between an upper stop 58 and a lower stop 59. A link GII is supported in a recess in the lower end of the armature 51 by a pivot 6I and this link 30 is provided with a lost-motion slot 62 engaging the hinge pin 54 of the toggle mechanism 52, 5l. Mounted in the housing, also, is a stop or cam member B3, which is mounted in the path of the hinge or 'any other suitable portion ofthe toggle 35 -mechanism 52, 53, when moving to circuit-opening position, for a purpose to be described more fully hereinafter.

The operation of the above-described operating, latching and tripping mechanism may be 40 understood by following the movements of the several elements in a cycle of operation from circuit-opening position, with deenergized electromagnet, as illustrated in Fig. 3; to circuitclosing position with electromagnet energized, as 45 shown in Fig. 4; to latched-in circuit-closed position with electromagnet deenergized, as represented in Fig. 5; and, iinally, to circuit-opening position by operation of the tripping mechanism with the electromagnet energized, as illustrated in Fig. 6.

The changes in the positions of the elements of the operating mechanism when moving from the position represented by Fig. 3 to that represented by Fig. 4, in response to the energization of elec- 55 tromagnet 30, 3 I, will be well understood by those skilled in the art. As the electromagnet Il), 3| attracts the armature 51 into its upper position illustrated in Fig. 4, the lower end of the lostmotion slot 62 engages the hinge pin 54 of the 50 toggle mechanism 52, 53, separating the pivots 55 and 56 with a force multiplying action and rotating the operating crank 40 and its attached shaft 6 in a counter-clockwise direction, as shown in Figs. 3 and 4, to bring the movable contacts 3 into 65 engagement with the stationary contacts 2, as shown in Fig. 2. The link 60 raises the hinge piny of the toggle mechanism- 52-53 slightly across dead center, when the spring 42 and the momentum of the moving parts .are effective to tendy to A biasing Spring 48 -5 position and the eiectromagnet l5, 8i may be deenergised, allowing yits amature 51 to fall, as shown in Fig. 5. The hinge pin t4 moves in the lost-motion slot 82 of the link 5l so that the fall tions oi' the other elements of the operating and -latching mechanism. It wi.l be noted that, during this closing operation of the breaker, the latch member 4B remains stationary, so that its closing mechanism.

In case an abnormally large current should flow in the circuitl of any of the cooperating pairs of contacts 2, I, for an interval of time determined by the setting of the time-delay mechanism 22, or in case the operating coil 21Y should be energized to trip the circuit interrupter in response to any predetermined condition. one of the several trip rods I9 will strike its cooperating tripping arm III attached to the trip shaft I4 and will rotate it in a counter-clockwise direction, as referred to Fig. 2, or in a clockwise direction, as referred to Figs. 3, 4, and `6;

Referring more particularly to Fig. 5, as the the latch member 45y disengagesthe detent'45 in theouter end of the arm 44 and the force of the biasing spring 42 rotates theA crank arm 40 and the bell-crank 43 in a; clockwise direction, each Fig. 6. Under these conditions, it will be noted that the 'crank arm 4II again engages its stop 4I and has moved the contacts 3, attached to the operating shaft 5, to circuit-opening position. During this movement between the positions i1- lustrated in Figs. k5 and 6, the hingerof the toggle mechanism 52, 53, or any other suitable engaging surface thereof, strikes and slides along the cam surface 54 of the stop member 53, which is such as to move the hinge from its over-center position to one in which it 'may be collapsed downwardly. While in Fig. 6 the armature 51 is illustrated in the position corresponding to the energization of the electromagnet 3U. 3|, so that, the toggle 52, 53 is restrained from completely collapsing, the movement of the several elements of the operating mechanism would be substantially the same if the electromagnet 30, 3l were deenergized, corresponding to the position of the armature 51 represented in Fig. 5. In this latter case, the link Bil would merely swing to the right through the larger angle, the hinge pin 54 of the toggle mechanism sliding in the lost-motion slot 52. Thus, the toggle mechanism would be free to collapse, as it is upon subsequent deenergization of the electromagnet 30, 3l, in the position shown in Fig. 6. Thus, it is seen that the movement of the crank arm 40 and that of the movable contacts of the circuit interrupter, upon disengagement of the latch member 45 .and the bell-crank 43, is completely independent of the position of the armature 51 and itsconnected operating link 60. In other words, the movable contacts and their connected mechanism are completely trip-free' of the operating mechanism. It will be noted that; in the above-described opening operation of the operating mechanism, the initial opening force is transmitted to rotate the biasing spring 42 operating through the toggle mechanism 52, 53 and the pin 55. The lever arm of this force operating on the pin 56 about the pin 55 is, necessarily, very small in order to minimize the tripping force required to disengage the latch 46 from the arm 45. If fricof the armature l1 has no eifect upon vthe posioperation is independent of the operation of the l trip shaft I4 is rotated in a clockwise direction,

about its respective axis, to the position shown in s the bell-crank 43 about its pivot 50 by virtue of 4 tion is present to a substantialdegree, as would be the case if the stop member to limit the upperf travel of the hinge of the toggle `mechanism/52,` 53 were a part of the stationary housing strucf' ture, it might sometimes occur that this opening 5` force acting about such a smalllever armlinight"v be ineffective to open the breakerv against' the iricticnal resistance.- y By incorporating the stops i 5ta-51a in the toggle mechanism itself, however, this frictional resistance is reduced to alo minimum and comprises only the rotational re#-` sistance at the several pivots. This arrangement thus insures reliable opening of the f circuitv breaker in response to the tripping of thelatch 45.

As the operating mechanism returns to .circuit opening position, 'and as the electromagnet 30, 3| is deenergized to allow the armature 51 and linkv 60 Vto fall, the spring 48 rotates the bell-crank 43 in a counter-clockwise direction so that the `dc.-

tent 45 automatically reengages the latch mem- 2o ber 46,. This arrangement forV engagement of the latch before the initiation of the successive closing operation of the breaker eliminates thel possibility o f any hammer blow or jar tendirigto in-i jure the latched surfaces or alter their position during the closing movement, and tends `to make f l the operation of the latching mechanism Lmore reliable. It willbe noticed that the latclr can be released'at anytime irrespective of the y'position of the closing mechanism,` so that the breaker is not only trip-free from the initial touching oly the contacts, but also vfor `all other positions of the closing mechanism; that is, Lthe latch may be maintained positively disengaged so that it is impossible to touch the contacts even momentarily.

While we have illustrated an electromagnet 30, 3| and cooperating armature 51 for actuating the operating link 50, it will be readily apparent that this link may be actuated manually or by any other suitable electrical or mechanical means;

While we have illi strated our invention as applied to a 3-pole circuit interrupter of the air-v break type, it will be obvious t-o those skilled in the art that it is equally suitable for application to circuit interrupters generally of any of the well-known types and of any number of poles.

While we have described what we at present consider the preferred embodiment of our invention, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from our invention,v and we therefore aim in the appended claims to cover all such changes and modications as fall within the true spirit and scope of our invention.

What we claim is:

l. An electric circuit interrupter comprising a base member, a stationary contact mounted thereon, a pivotally mounted actuating shaft, a movable contact supported therefrom, an operating crank arm engaging said shaft, a. bell-crank member, a latch member normally engaging an arml of said bell-crank member to restrain it from motion about its pivot, a toggle mechanism interconnecting said crank arm and said bellcrank and provided with an operating pin, an elec- G5 l 'g-tive normal positions and to secure a reengagement therebetween.

.I 2.' An electric circuit interrupter comprising a basev member, a plurality of stationary contacts mounted thereon, a pivotally mounted actuating shaft, a plurality of movable contacts supported 1 therefrom and disposed, upon angular movement thereof, to engage corresponding stationary con tacts, an operating crank engaging said shaft, a bell-crank member, a latch member normally engaging an arm-of said bell-crank member to restrain it from motion about its pivot, a toggle mechanism interconnecting said crank arm and said bell-crank and provided with an operating pin,'an electromagnet provided with a movable amature, an operating link connected to said armature and provided with a lost-motion slot engaging said operating pin, whereby energization of said electromagnet is effective to operate said toggle mechanism to overcenter position and move said contacts into engagement, stop means yfor limiting the travel of. said toggle in overcenter direction, separate means responsive to abnormal conditions in the circuit associated with each pair of cooperating contacts. a trip shaft responsive to the operation of any of said lastnamed means and uponwhich is mounted said latch member, biasing means eilective, upon operation of said tripping means, to move said bell- ,crank andits connected toggle mechanism and turn said bell-crank and said latch member to,

their respective normal positions and to eiIect their reengagement.

3.v In an electric circuit interrupter comprising movable and stationary contacts, operating mechanism for said movable contact comprising an electromagnet provided with a movable armature, an actuating member for connection to said movable contact, a latching mechanism normally restrained from motion, a linkage mechanism interconnecting said actuating member and said latching mechanism and provided with an operating pin, an operating link connected to said armature and provided with a lost-motion slot engaging said operating pin,v whereby energization of said eleetromagnet is effective to operate said movable contact to circuit-closing position, means for tripping said latching mechanism, and biasing means effective to move said latching mechanism and its connected members and cause a movement of said movable contact to circuitopening position upon the operation of said tripping means.

4. In an electric circuit interrupter comprising movable and stationary contacts, operating mechanism for said movable contact comprising an electromagnet provided with a movable armaiure, an actuating member for connection to said movable contact, a pivotally mounted auxiliary member, force multiplying mechanism interconnecting said actuating member and said pivotally mounted member and provided with an operat-l ing pin, an operating link pivotally connected to said armature and provided with a lost-motion slot engaging said operating pin, a latch member normally engaging said auxiliary member and restraining it from rotation about its l pivot, whereby energization of said electromagnet is eiiective to operate said movable contact to circuit-closing position through said force multiplying mechanism, means for disengaging said 1 latch member and 'said auxiliary member, and biasing means effective .to rotate said auxiliary member about its pivot and cause a movement of said movable contact and said interconnecting mechanism to circuit opening position upon oper- 'l ation of said disengaging means. 5. In an electric circuit interrupter comprising movable and stationary contacts, operating mechanism for said movable contact comprising an actuating member for connection to said movable contact, n. bell-crank member, a latch member normalLv engaging an arm of said bellcrankv member to restrain it from motion about its pivot, a toggle mechanism interconnecting said actuating member and the other arm of said .A bell-crank member, means for extending said toggle mechanism and operating it to an overcenter position to operate said movable contact to circuit-closing position, means for disengaging said latch member and said bell-crank mem-V y ber, and biasing means effective, upon operation of said disengaging means, to rotate said bell-crank about its pivot and cause a movement of said movable contact to circuit-opening position. 4 6. In an electric circuit interrupter comprising movable and stationary contacts, operating mechanism for said movable contactv comprising an actuating member for connection' to said movable contact, a latching mechanism normally 45 restrained from motion, a toggle mechanism interconnecting said actuating member and said latching mechanism, means forextending said toggle mechanism and operating it to an overcenter position to operate said movable contact 50 to circuit-closing position, means for tripping said latch mechanism, biasing means effective, upon operation of said tripping means, to move said latching mechanism and its connected toggle mechanism and cause a movement of said mov- 55 able contact to circuit-opening position, and a cam surface disposed in the path of motion of a member of said toggle mechanism during the v above-mentioned tripping operation and eiective to break said toggle mechanism. 60

'7. In an electric circuit interrupter comprising movable and stationary contacts, operating mechanism for said movable contact comprising an actuating member for connection to said movable contact, a latching mechanism normally 65 restrained from motion, a toggle mechanism interconnecting said actuating member and said latching mechanism, means for extending said toggle mechanism and operating it to an overcenter position to operate said movable contact to 70 circuit-closing position, means for limiting the movement of said toggle mechanism in an overcenter direction, whereby said movable contact is latched in circuit-closing' position, means for tripping said latch mechanism, a spring connected to bias said movable contact and effective, upon operation of said tripping means, to move said latching mechanism and its connected toggle mechanism and cause a movement of said movable contact to circuit-opening position, and a cam surface disposedin the path of motion of the intermediate pivot of said toggle mechanism during the above-mentioned tripping operation and efl'ective to break said toggle mechanism from its 'overcenter position.

8. In an electric circuit interrupter comprising.

movable and stationary contacts, operating mechanism for said movable contact comprising an actuating member for connection to said movable contact, a bell-crank member, a latch member normally engaging an arm of said bell-crank member to restrain it from motion about its pivot, a toggle mechanism interconnecting said actuating member and-the other arm of said bell-crank member, means for extending said toggle mechanism and operating it to an overcenterposition to operate said movable contact to'circuit-closing position, means independent of said operating mechanism and of any stationary parts oi.' said l,interrupter for limiting the motion oi' said toggle mechanism in an overcenter direction, means for disengaging said latch member and said bellcrank member, and biasing means eective, upon operation of said disengaging means, to rotate said bell-crank about its pivot and cause a movement of said movable contact to circuit-opening position. l

9. AIn -an electric circuit interrupter comprising movable and stationary contacts, operating mechanism for said movable contact comprising an actuating member for connection to said movable contact, a bell-crank member, `a latch membernormally engaging an arm of said bell-crank member to restrain it from motion about its pivot, a toggle mechanism interconnecting said actuating member and the other arm of 'said bellcranl; member, means for extending said toggle mechanism and operating it to an overcenter position to operate said movable contact to circuit-closing position, cooperating stop members carried by the links of said toggle mechanism for limiting the motion oi said toggle mechanism in an overcenter direction, means for. disengaging said latch member and said bell-crank member, and biasing means eilective, upon operation of said disengaging means, torotate said bell-crank about its pivot and cause a movement of said movable contact to circuit-opening position.

10. In an electric circuit interrupter compris- Y ing movable and stationary contacts, operating mechanism for said movable contact vcomprising an actuating memberior connection to said 'movablecontact a bell-crank member, a latch member normally engaging an arm o! said bell-crank member'.to restrain it from m0- ,tion about its pivot, a toggle mechanism interconnecting said actuating member and theother arm ot said bell-crank member, means for extending said toggle mechanism and operating it to a slightly overcenter position in operate said movable contact to circuit closing position. means independent of said operating mechanism and oi- -any stationary parts oi said interrupter for limiting the travel oi' said toggle in an overcenter direction. said extending means im- Y parting a momentum to said toggle mechanism aiding in its travel i'romsaid overcenter position to a position determined by said limiting means, means for disengaging'said latch member and said bell-crank member, and biasing means eilective, upon operation oi said disengaging means, to rotate said bell-crank about its pivot e and cause a movement oi said movable contact to circuit-opening position.

11. In an electric circuit interrupter, comprising movable and stationary contacts, operating mechanism for said movable contact comprising i an actuating member for connection to said movable contact, a bell-crank member, a latch member normally engaging an'arm of said bell-crank member to restrain it from rotation about its pivot, a toggle mechanism interconnecting said lliV contact to circuit-opening position, and an auxgA iliary biasing spring interconnecting said bellcrank and said latch member andoperative, upon the collapse oi' said toggle mechanism, to return said bell-crank `to its normal position after a circuit-opening operation, and to effect the relai) engagement between said latch member and said bell-crank.

l2. In an electric circuit interrupter comprising movable and stationary contacts, operating mechanism for said movable contact comprising an actuating member for connection to said movable contact, a latching mechanism normally Y restrained from motion, a toggle mechanism interconnecting said actuating member and said latching mechanism, means for extending said 40 toggle mechanism and` operating it to an overcenter position to operate said movable contact to circuit-closing position, means for tripping saidlatch mechanism, biasing means eiIective, upon operation oi said tripping means, to Vmove said latching mechanism and its connected toggle mechanism and cause a movement of said movable contact to circuit-opening position, and means disposed in the path of motion of a member of said toggle mechanism during the above-mentioned tripping operation and eifective positively to break said toggle mechanism.

13. In an electric circuit interrupter comprising movable and stationary contacts, operating mechanism for said movable contact comprising an actuating member for connection to said movable contact, a three-element toggle mechanism connected to operate said actuating member and normally having both hinges on thesame side of4 center, one end link of said toggle mechanism 00 comprising a latch element. a latch member normally engaging said latch element to restrain 'r c. oaavrs. Jn. o'rro JnNsnN. 

